A glow plug is used as an assisting heat source in internal combustion engines of the compression ignition system, such as Diesel engines. The glow plug includes: for example, a heater configured to heat a combustion chamber in an internal combustion engine; a pressure sensor configured to measure the pressure in the combustion chamber; and a coupling member in a thin film shape joined with the heater and with a housing and configured to hold the heater in a displaceable manner in an axis line direction of the glow plug. In this glow plug, the pressure sensor detects a load applied to the pressure sensor by displacement of the heater according to a change in pressure in the combustion chamber.